Conventionally, drug manufacture can involve a plurality of drugs being manufactured on one production line. In this case, when the manufacture of one drug ends, the production line is cleaned, and a different drug is manufactured. Cleaning of a production line is described in Patent Literature 1, for example. However, in order to check that none of the drug that was previously manufactured remains after the production line has been cleaned, the residual amount of the drug is computed by wiping a predetermined location of the line with a test substance and analyzing the test substance.